I think Facebook has a strong motivation to tailor the newsfeed algorithm to keep you longer on Facebook, see more ads, generate more clicks and revenue etc, so there might be a case to be made in order to engage you more, the algorithm should show you more content you like or tend to agree with than ones you would not want to engage with (remember Facebook doesn't have a dislike button), so I think its not really a great place to meet most people of dissenting views to yours, I would actually speculate that its probably the other way around, Facebook is one fo the places where you meet most people sharing the same views as yours.
/0.2$
edit: typo